Cervical mucus (CM) undergoes changes during the normal menstrual cycle as a result of which sperm cannot penetrate the cervix. This represents a physiological method of contraception. The specific change(s) in CM which alter sperm penetrability (as opposed to the many changes induced by steroid hormones) are virtually unknown. The proposed research is directed to identification of changes in electrolyte concentration and distribution in CM associated with sperm penetrability. Energy dispersive X-ray analysis and scanning electron microscopy (SEM/EDX) when combined with conventional tests for CM 'quality' and penetrability is a novel method which, for the first time, will permit such an investigation. Electrolyte and protein content of means of influencing sperm penetrability in vitro. This research represents a pilot study to establish the feasibility of this approach to fertility control. Such a physiological method of fertility control would offer significant advantages, in terms of reduced clinical and psychological side effects, over currently available methods.